Known impellers used for centrifugal compressors and mixed flow compressors typically include open impellers without a shroud and shrouded impellers with a shroud.
A shrouded impeller is known to be advantageous over an open impeller in that it has a high compression efficiency with, for example, a low flow loss because it has no gap between impeller blades and a casing accommodating the impeller.
On the other hand, a shrouded impeller has a problem in that it is less easily produced than an open impeller because it has a shroud.
Methods proposed for solving the problem described above include a method in which a hub and blades and a shroud are separately formed, and the blades and the shroud are bonded; a method in which a shrouded impeller is integrally formed by machining; and a method in which an impeller is formed as an inner segment and an outer segment, and the two segments are bonded (see, for example, Patent Literatures 1 and 2).